Ballast structure having filament windings remote from the other windings



July 6, 1965 A. E. FEINBERG 3,193,723

BALLAST STRUCTURE HAVING FILAMENT WINDINGS REMOTE FROM THE OTHER WINDINGS Filed Dec. 15, 1961 3 Sheets-Sheet l a mmec a July 6, 1965 A. E. FEINBERG 3,193,723

BALLAST STRUCTURE HAVING FILAMENT WINDINGS REMOTE FROM THE OTHER WINDINGS Filed Dec. 15, 1961 3 Sheets-Sheet 2 gjjm w 1/ July 6, 1965 A. E. FEINBERG 3,193,723

BALLAST STRUCTURE HAVING FILAMENT WINDINGS REMQTE FROM THE OTHER WINDINGS Filed Dec. 15. 1961 3 Sheets-Sheet 3 IV I afformegfi United States Patent 3,193,723 BALLAST STRUCTURE HAVING FILAMENT WINDINGS REMOTE FROM THE OTHER WINDINGS Albert E. Feinberg, Chicago,lll., assignor to Advance Transformer Co., Chicago, 11L, a corporation of Illinois Filed Dec. 15, 1961, Ser. No. 159,563 11 Claims; (CL 315-97) This invention relates generally to a ballast structure and more particularly is concerned with the construction of a ballast which is designed to provide proper igniting and operating voltages for gaseous discharge devices which have filaments that are energized continuously.

The gaseous discharge devices with which this invention is concerned comprise fluorescent lamps, each such lamp being formed of an elongate glass tube or envelope having an atmosphere of argon and perhaps other inert gases therein under low pressure and a few droplets of mercury to provide an ionizable gas. An oxide coated filament is sealed in each end, and the lamp is adapted to be connected across a source of high voltage whose purpose is to provide ignition voltage for the gaseous atmosphere in the lamp. As soon as the mercury gas in the envelope ionizes as an electrical discharge, the lamp passes current in large quantities. It requires considerably higher voltage to ignite the lamp than it does to maintain the arc, but the impedance of the lamp at open circuit conditions is very high, while the impedance during discharge is quite low. A transformer is usually used to raise the line voltage, if the latter is lower than ignition voltage of the lamp, and some reactive means is used to provide a high impedance externally of the lamp when current flows to limit this current to a safe value not destructive to the lamp, filaments or the windings of the transformer.

in recent years it has become recognized that the various functions required in apparatus for igniting and thereafter operating the lamp can be obtained through the use of a high leakage reactance transformer, that is, one in which leakage is deliberately built into the transformer. On open circuit such a transformer provides a high voltage in combination with one or more secondaries,the summation of which is substantially independent of the presence of. shunts used to provide the high leakage react-' ance. This high voltage is applied across the lamp which ignites and commences to pass current. As soon as current flows through the windings of the transformer, the leakage reactance comes into play and impedes the flow of current and decreases the voltage. Various circuits and magnetic core structures have been used to accomplish this.

One of the most widely used fluorescent lamps today is a lamp with rugged and durable filament construction that can carry a relatively high current flow at all times, as opposed to the so-called pre-heat start lamps of several years ago which could not withstand the filament current combined with the normal fiow of current through the lamp when ignited for any substantial length of time. Pre-heat start lamps had special starter circuits which enabled current to fiow through the filaments during the starting period to create clouds of electrons in the vicinity of the filaments and thereby reduce the voltage required to ignite the lamp. Thereafter the starter device opened the filament circuit so that the only current flowing through the filaments was the lamp current without the addition of the filament current. Actually in the pre-heat start lamps, the operating current flowed through one leg of the filament. The modern lamp is known in the United States as the rapid start lamp, and it is capable of carrying the continuous filament current of the ordinary filament winding provided on a transformer in addition to the operating current of the lamp itself.

In the United States there are no limitations upon the amount of current that will be carried by any lead to a cathode, that is, by either conductorwhich connects with the filament. The ordinary rapid start lamp ballast in the United States will have the filament windings wound directly upon the primary winding, or even in the form of tapped portions of the primary winding, so that the current flowing in one lead of the filament is certain to be close to the arithmetic sum of the lamp current and the filament current due to direct coupling of filament winding and primary winding. 7

Outside of the United States, the requirements of ballasts for available lamps havebeen established by the International Electro-technical Commission. Reference may be had, for example, to Publication 81, second edition, dated 1961. On page 45 of this document electrical characteristics of lamps equivalent to those known as rapid start in the United States are set forth. The difficulty which the invention herein solves is in connection with the lamps designatedlamps with High Resistance Cathodes. The high power lamp rated at watts requires that the maximum current in any lead to a cathode be 1.60 amperes. This requirement cannot be met by conventional methods of winding the filament winding upon the primary winding, because the current required by a high resistance filament is much higher than ordinary, and this combined with the operating or running current for this 80 watt lamp, for example, will certainly exceed 1.60

amperes.

The primary and basic object of the invention herein is to provide a ballast to ignite and operate thegaseous discharge lamps which use high filament current and carry a high running current, which has filament windings for the lamps, but which provides a current flowing in the filaments during operation thereof which is substantially less than the arithmetic sum of the currents in the filament and the lamp.

The mannerin which the primary object is accomplished in the invention herein is also of note, since it is another object of the invention. The filament current and the lamp current are provided by the ballast in such a manner that there is a substantial phase angle between them so that they combine vectorially to produce a resultant or total current the value of which is substantially less than the arithmetic sum of these currents.

A further object of the invention is to provide the particular ballast structure which will accomplish the results mentioned above, and to provide such structure which is simple and compact and economical to manufacture and assemble. I I

Prior to entering upon a detail description of the preferred embodiments of the invention as required by the patent statues, it is desired to make reference to the particular manner in which the objects of the invention are accomplished structure-wise with respect to a phase of the invention which may not readily be appreciated without some emphasis. The maximum benefit to the using public for any product is achieved when that product is produced in a manner which enables that product to be sold as economically as possible. Then the degree of success for the accomplishment is measured by the economic circumstance of the humblest person purchas mg.

This is perhaps an over-simplification of an economic truism which is not ordinarily considered because it is unusual to relate it to invention. In this case, the de sideratum is to accomplish the desired results, but to accomplish them in such a manner as to keep the cost of the resulting device as close as possible to devices which do not use the invention. In the invention herein, this a was one of the most important consideration of all, because, there may be other ways of accomplishing what is sought, but only with great expense and complexity and accompanying increase in cost. One method which has been used is to provide a circuit which decreases the filament current as soon as the lamp ignites, is shown for example in Lemmers Patent 2,594,549, but the expense and complexity of this structure is obvious.

The ballast of the invention herein can be, and actually has been, constructed upon laminated cores which are stock structures that have been used in other ballasts and are adapted to the ballast of the invention without modification. The windings or the ballast of the invention are formed in the same manner as other ballasts, upon conventional coil winders in conventional methods and with the same handling and treatment that are wellknown. The mounting of the wound coils upon the winding leg of the ballast of the invention and the arrangement thereof are according to known methods, and the connection of the windings together and the leading of the same out of the ballast are in accordance with conventional practice. The number of leads and their external connection with the lamps is no difierent than in the case of other ballasts so that the user has no unusual problems in setting the ballast into a circuit for operation.

Because of the above, the ballast of the invention can be made upon the same production line and with the same apparatus, materials and methods as other ballasts, with no more difficulty in setting up than occasioned by a routine change in the details of a conventional ballast upon the production line.

The same reference characters will be used throughout the several views of the drawings wherever possible for ease of identification of the same or equivalent components.

In the drawings:

FIG. 1 is a circuit diagram of the invention showing the ballast being connected to a pair of fluorescent lamps having filaments or cathodes.

FIG. 2 is a semi-diagrammatic view of a ballast constructed in accordance with the invention, illustrating the laminated core in plan and the windings in section.

FIG. 2a is a fragmentary view of the left hand end of a ballast similar to that of FIG. 2 but of modified form.

FIG. 3 is a partial circuit diagram of a modified form of filament winding connection suitable for use with the circuit of FIG. 1 and with other similar circuits.

FIG. 4 is another filament winding connection diagram similar to that of FIG. 3 but of a further modification.

FIG. 5 is a circuit diagram similar to that of FIG. 1 but of a modified form of the invention.

FIG. 6 is a view similar to that of FIG. 2 but of a modified form of the invention.

FIG. 7 is a vector diagram used to explain the theory of the invention.

PEG. 8 is a view similar to that of FIG. 2 but illustrating another modified form of the invention, intended for use with a single lamp.

FIG. 9 is a circuit diagram of a system using the ballast of FIG. 8.

As indicated above, the invention is based upon the theory that the resultant current flowing in the leads of the filaments of the gaseous discharge lamp can be made up of the vectorial addition of a plurality of currents whose arithmetic sum, i.e., addition without regard to phase relationship, would otherwise exceed the said resultant current by a substantial amount. The manner of accomplishing this is to loosely couple the filament windings to the primary windings by interjecting a high reluctance shunt between them whereby to provide leakage reactance between the primary winding and the filament windings, the effect of which is felt only after the lamps have become ignited. The primary winding is still arranged to serve the high leakage secondary winding to achieve the leakage reactance needed to decrease the lamp voltage after ignition and ballast the lamp to decrease the flow of current.

In FIG. 1 there is illustrated a lighting circuit which is designated generally fill that embodies the invention; the transformer 12 which is used in connection therewith is shown in FIG. 2. The majority of the circuit per se is a familiar one, in which the lamps L and L are started in sequence in that order, and then are operated in series. Looking, for the moment, at the known portion of the circuit, each lamp has a filament sealed in its ends providing, therefore, filaments 14 and 15 in lamp L and the filaments l6 and 17 in lamp L The filaments are connected by leads lid, 19, 2.6, 21, 22 and to three filament windings F F and F which are inductively associated with the primary winding P on the transformer core. The inductive arrangement and the construction of the transformer are not known, and this forms the crux of the invention.

Continuing with the circuit per se, the primary winding P is connected across a source of AC. voltage such as, for example, a 120 volt main, or in certain cases a 240 volt main, designated 25. The secondary winding S has one terminal connected to the right hand terminal of the primary winding, this juncture 26 being connected to one side of the line and also by way of the lead 27 to the filament 14-. The right hand terminal of the secondary winding S is connected by the lead 28 through a series condenser C to a terminal of the filament 17. The filaments l5 and 1d are arranged in parallel by the jumpers 3i? and 31 which are connected respectively to the leads Eli and 21 so that the filament winding F serves two filaments. The shunt circuit 32 with its starting capacitor C connects between jumper 36 and the lead 28. The lead 23 connects with the lead 28 also.

An analysis of the circuit will show that the only voltage that is applied to the lamps L and L is that developed across the secondary winding S, the voltage of the primary winding P being excluded by virtue of the arrangement. Thus, when the primary winding P is energized; current commences to flow in the filaments and a voltage is induced across the secondary winding S which appears across the lamp L The condensers C and C are ineffective as impedances on open circuit. As soon as lamp L ignites, the flow of current resulting through the bypass circuit 32 develops a voltage across the condenser C sufficient to ignite lamp L after which current fiow through lamp L will short circuit the condenser C Current thereafter will flow through the lamps, the secondary S and the capacitor C resulting in a leading current as preferred. The transformer 12 is a straight transformer, in this circuit, as opposed to an auto-transformer in which the voltage of the primary directly contributes to the voltage across the load.

Note that if the filament windings F F and F still continue to provide current for the filaments, and there is no structure to prevent this, certain filament leads, such as for example 35 and 36 will be carrying, not only the total lamp current but the filament current in that filament as well. While the external connections to the lamps may be made of any desired size of wire, the lamps themselves have limitations on the conductors from which the filaments are formed, and these are the reason for the limited current required according to the specificaticns mentioned above.

Before proceeding further with the description, it should be apparent that even where the requirements for the total current flow in a filament conductor are capable of being met by conventional structures, the use of the structure of the invention will serve to reduce the total current fiowing in the filament leads thereby lowering the cathode dissipation and increasing the life of the lamps.

According to the invention, the windings are all mounted upon an elongate shell type core 38 of a construction such as shown in FIG. 2. There is a central winding leg tilwhich is of T-shaped configuration having a cross bar 42 at the left hand end in the view, and two L-shaped side legs 44 the short arms 46 of which abut against opposite edges respectively of the right hand end of the central winding leg forming the non-gapped joints 48. The cross bar 42 also engages the left hand ends of the side legs 44 at the non-gapped joints 50. The parts 40 and 44 are formed of stacks of laminations of identical configuration held together by rivets or the like and/ or clamped in assembly by suitable sheet metal clamps (not shown) engaging the corner notches shown at 52. The individual laminations are stamped from electrical sheet steel in a so-called scrapless method in which the T-shaped and L--sl1aped parts are matingly engaged. When the stacks of individual laminations are assembled to form the core 38, they are arranged as shown. The technique is in common use today, and is well-known.

The absence of gaps at joints 48 is compensated for by the presence of a central slot at 56. Since the secondary winding S will be carrying a leading current during operation of the lamps, there is a need for a bridged gap in the core carrying the secondary flux to prevent saturation and maintain correct lamp current wave shape.

The primary winding P is mounted on the central winding leg in the center of the core 38, that is, between the ends of the winding leg 40. The secondary winding S is butted against the primary winding P, but the normal end spaces which are required in a practical coil will provide finite spacing between these windings. In addition, since the particular structure is quite elongate, obviously the portions of the secondary winding which are remote from the primary winding P will have substantially less coupling with the primary winding than those portions which are contiguous thereto. The secondary winding S is therefore loosely coupled with .the primary winding and high leakage reactance will be developed in the secondary winding during operation. If necessary, a magnetic shunt of high reluctance with a suitable gap can be inserted between the primary winding P and the secondary winding S. I

The filament windings F F and F are all mounted as shown in the extreme left hand end of the central winding leg 40 and are separated from the primary by a substantial space. This space is filled with a bundle of laminations 53, there being such a bundle on each of the opposite sides of the central winding leg. Narrow gaps are provided at 60 to increase the reluctance of the resulting shunt 8H The filament windings are mounted on the same form and preferably mechanically secured together to assist in handling, which is in accordance with common practice. For example, the total sum of windings is wound upon a single form with the usual interlayer insulation, and in addition to the end terminals, two loops are pulled out of the windings at suitable layers to divide the total layer-s into the three windings. Each loop is cut to form terminals of adjacent filament windings. Obviously independent coils can be wound and mounted in the same space.

The result of separating the filament windings F F and F from the primary winding P is to cause the current flowing in the filaments to lag the primary voltage. In FIG. 7, which is not to scale, but is a generalization based upon what is believed to be the theory of operation of the apparatus, E is the primary voltage, and I is the filament current, shown lagging by a substantial angle y which has been measured as 40 in some cases. The circuit with which the apparatus is intended to be used includes a capacitor C that is of greater capacitive reactance than the inductive reactance of the secondary Winding S during operation so that the lamp arc current I leads the primary voltage E by a substantial angle 6.

One can see that by a simple vectorial resolution, the resultant total current I flowing in the filament leads will be substantially less as for its actual value than the arithmetic sum of l -H The angle x= +6 between the filament current I and the lamp current I will be of the order of 90 and the vector diagram is drawn in this manner, but obviously there will be considerable variation between structures. The sense of the instantaneous voltages of the filaments relative to the instantaneous secondary voltage will have little or no effect upon the operation of the device in cases where the angle or is about 90 because if one reverses the polarity of the filament windings F F and F as by interchanging their terminal connections relative to the connections of the secondary winding S, the angle 5 between the new filament current I and I will also be of the same order, giving rise to a resultant current I that is approximately the same as the current I The builder of the particular ballast can try both polarities and use the one which gives the best characteristics, considering current balance in the lamps, starting efl ects and operating efiects.

To give some idea of the values of a typical structure, the transformer 12 of FIG. 2 was drawn to scale, with the overall length 7.63 inches, the total Width 3.05 inches, the length of the space occupied by the filament windings along the central winding leg inch, the shunt Kainch, the primary winding'P about 2 inches and the secondary winding about 3% inches. The stack height was 1% inches. The primary winding was 754 turns of 22 gauge wire, the secondary was 1352 turns of 22 gauge wire and the filaments were 60 turns each of 22 gauge wire. The lamps were watt lamps. The condenser C was .09 microfarad and the condenser C was 6.65 microfarads, with a suitable voltage rating of-405 volts. The gaps 60 were .010 inch each. I

For this structure, the lamp current was of the order of .860 ampere and the filament current prior to ignition was of the order of .800 ampere. The total lamp current in the filament leads after ignition was found to be approximately 1 to 1.1 amperes, which is substantially less than the sum of .8 and .86. Note that when compared with the requirements of the publication above referred to the sum 1.66 is somewhat above the maximum permissible value of 1.60 while the actual current produced in the structure of the invention is very substantially below the value 1.60 without losing any of the benefits of the high filament current needed for reliable starting.

The laminations of transformer 12. have small unnumbored notches in their inner edges, merely for identification of the original mating sides.

In FIG. 2a there is illustrated a fragment of a transformer 12 which may be practically the same as transformer 12 but for certain variations. Instead of the assembly of the laminations into a T-shaped central leg 40 and L-shaped side par-ts 44, the core 33' is formed of a rectangular shell having bridging ends 42' and elongate integral sides 44. The central winding leg 40' is made up of a stack of laminations punched out of the lamina-, tions which form the outer shell. Openings in the shell provide the windows for windings on opposite sides of the central winding leg. The windings are pre-mounted upon the central leg 40' which is then forced into the center of the shell. No clamps are needed to keep the core parts together as in the ballast 12.

7 ,FIG, 2:: also illustrates another modification. The slot 64 which is provided under the filament windings F, F and B, provides additional de-coupling of the filament windings relative to the primary. This slot could also be used in the ballast 12. The use of the slot enables the gaps 60 to be increased in size over the gaps 60, which are .010 inch. Thus the presence of such a gap makes manufacture easier because of decrease of c-riticality of gap dimsensions.

FIGS. 3 and 4 illustrate two variations in connecting the filament winding F to the filaments 15 and 16. In FIG. 3, the filaments 15 and 16 are connected in series with each other and with the filament winding. Lead 31 of PEG. 1 is eliminated and the connections are somewhat simplified. In FIG. 4, the filament winding F is center tapped and a lead 31 connects from the tap to the lead 3%. In this circuit each half of the filament winding serves a different filament. Difierent variations can be used for different requirements. Obviously where more than two lamps are used, as feasible with the invention, each filament winding maybe requi ed to serve a multiple number of filaments.

Attention is now invited to FIGS. 5 and 6 which illustrate the circuit lltitl and the ballast transformer 112. In this structure the cross section of the ballast transformer 112 (drawn to approximately the same scale as ballast transformer 12) is more elongate than that of FIG. 2. The voltage used for ignition and operation of the lamps L and L is the combined voltages of the primary winding P and the secondary winding S and hence these are connected in auto-transformer relation ship. The left terminal 33 of the primary winding l connects by lead 34 and lead 35 to filament 14. The conductor 27 of FIG. 1 is eliminated. In all other respects the circuits of 10 and 1% are the same. In the structure mil, the windings P and S must be connected additive, voltage-wise.

In the case of the transformer core 38 of FIG. 6, this is a scrapless type of core made of T-shaped laminations stacked and secured together to form the center win-ding leg 4i) and F-shaped laminations stacked and secured together to form the side parts 44. The shunt 8H is formed by the central projections 58 of the side parts 44 and the notches 64- resulting during the punching of the T-shaped and F-shaped laminations in mated configuration, provided a substantial reduced diameter section in the central winding leg 40 to 59. The notches 6d are the equivalent of the slot 64 of FIG. 2. These make the transformer easier to manufacture because larger air gaps oil may be provided at the shunts 8H The increase in leakage reactance can be compensated for by increasing the number of filament winding turns. The resistance of the filament windings is so low compared with that of the actual filaments that there is no concern about changing operating characteristics because of added turns.

The invention is applicable to single lamp ballasts such as that shown at 2% in FIGS. 8 and 9. These figures are also intended to show other variations in ballast transformer construction. Considering the circuit first, the lamp L is connected in auto-transformer arrangement with primary winding P and secondary winding S, using two filament windings F and F loosely coupled with the primary winding P. The secondary winding S is also loosely coupled with the prlmary winding P. In passing it might be mentioned that although no shunt such as 8H is shown in the other structures illustrated in FIGS. 1 through 6, it is not to be inferred that the secondary windings there are tightly coupled with their respective primaries.

In FIG. 8 there is illustrated a somewhat shortened ballast transformer 212 in which the coupling between the primary and secondary windings P and S is rendered loose by an additional shunt 8H The core 38 is formed of the central winding leg 46 which may have a slot 56 adapted to be disposed within the secondary winding S, and side framing members 44. The side members 44 have inwardly directed projections 46, 58, 58' and 42, in that order from left to right. Projections 46 abut the central winding leg 4h at gap-less joints 48; the projections 58 cooperate with the outwardly extending projections 61 formed on the central winding leg to form the shunt 8H with gaps 60; the projections 58 cooperate with the Sides of the central winding leg 48 to form shunt SH with gaps 60'; and the projections 42 abut sides of the central winding leg 40 at the right hand end thereof to form the gapless joints 5% The windings F and F are independently formed and slipped onto the central winding leg from the left, seating r.) against projections 61. The primary winding P is slipped onto the central winding leg 46 from the right and abutted against the right hand side of the projections 61. The central winding leg id is somewhat reduced in width at 7th to provide shoulders for locating the winding S.

The operation of the structure 2% is believed apparent from the illustration and the previous description. Another slot in the central winding leg under the filament windings F and F might be advantageous in certain cases.

it is believed that the invention has been fully described to enable those skilled in this art to understand and practice the same without added exposition. Many variations are capable of being readily made without departing from the spirit or scope of the invention as set forth in the appended claims.

What it is desired to secure by Letters Patent is:

1. In a ballast structure for use with a fluorescent lamp having cathodes in the lamp at the ends thereof and including a transformer for energizing the lamp and a primary winding and a secondary winding loosely coupled relative one another, means for connecting the primary winding to a source of alternating voltage, at least the secondary winding of said primary and secondary windings being connected across the cathodes, each cathode comprising a filament having a pair of conductors extending out of an end of the lamp envelope, and the filament windings inductively associated with the primary winding and respectively connected across a pair of conductors; the invention comprising:

an elongate iron core having a winding leg, a side leg and a gapped shunt comprising a magnetic circuit between the winding leg and the side leg, all of the filament windings being coaxially mounted on the winding leg on one side of the shunt and all of the other windings being coaxially mounted on the winding leg on the other side of the shunt, whereby the filament windings and the other windings have a loose magnetic coupling which will result in a substantial phase angle difference between the filament winding current and the secondary winding current.

2. The invention as claimed in claim 1 in which lead means are provided for connecting said secondary winding in circuit with said lamp including capacitive reactive means therein to cause the lamp current to lead the primary voltage.

3. The invention as claimed in claim 1 in which there is a decreased cross section area in the core beneath the filament winding.

4. The invention as claimed in claim 1 in which there is a second gapped shunt in the core between the primary and secondary windings.

5. A ballast structure as claimed in claim 1 in which said core has added means for decoupling the filament and primary windings.

6. The invention as claimed in claim 1 in which the primary winding is disposed on said core adjacent said gapped shunt so that the primary winding and gapped shunt separate the filament windings from the secondary winding.

'7'. A ballast structure for a pair of series connected gaseous discharge lamps having end filaments and including: an elongate iron core having three windows along the length thereof, a pair being adjacent one another and a gapped shunt spacing an end window from said pair, a plurality of windings coaxially mounted along the length of said core and forming a transformer therewith, there being a primary winding in one window of said pair adapted to be connected to a source of A.C. voltage, a secondary winding in the other window of said pair and having lead means including at least a series condenser for connecting same to said lamps for igniting and operating same, and a plurality of filament windings only disposed in said end window adapted to be connected with said filaments, whereby during operation of said lamps, a

high leakage reactance will be developed in said filament windings such that the current flowing in the filaments produced by said filament windings will be substantially out of phase With the lamp currents in said filaments.

8. A ballast structure as claimed in claim 7 in which the primary Winding is disposed in that window of said pair adjacent said shunt.

9. A ballast structure as claimed in claim 7 in which there is a bridged gap in said iron core adjacent said sec ondary winding.

10. A ballast structure as claimed in claim 7 in which said primary and secondary windings are connected in auto-transformer relation.

References Cited by the Examiner UNITED STATES PATENTS 2,802,143 8/57 Kobayashi 336-460 X 2,869,037 1/59 Brooks et al. 317-g-97 2,870,378 1/59 Abrahams 315-97 2,965,799 12/60 Brooks et al 315-97 2,971,124 2/61 Feinberg 31597 3,010,050 11/61 Hume et al 336165 GEORGE N. WESTBY, Primary Examiner. 

1. IN A BALLAST STRUCTURE FOR USE WITH A FLUORESCENT LAMP HAVING CATHODES IN THE LAMP AT THE ENDS THEREOF AND INCLUDING A TRANSFORMER FOR ENERGIZING THE LAMP AND A PRIMARY WINDING AND A SECONDARY WINDING LOOSELY COUPLED RELATIVE ONE ANOTHER, MEANS FOR CONNECTING THE PRIMARY WINDING TO A SOURCE OF ALTERNATING VOLTAGE, AT LEAST THE SECONDARY WINDING OF SAID PRIMARY AND SECONDARY WINDINGS BEING CONNECTED ACROSS THE CATHODES, EACH CATHODE COMPRISING A FILAMENT HAVING A PAIR OF CONDUCTORS EXTENDING OUT OF AN END OF THE LAMP ENVELOPE, AND THE FILAMENT WINDINGS INDUCTIVELY ASSOCIATED WITH THE PRIMARY WINDING AND RESPECTIVELY CONNECTED ACROSS A PAIR OF CONDUCTORS; THE INVENTION COMPRISING: AN ELONGATE IRON CORE HAVING A WINDING LEG, A SIDE LEG AND A GAPPED SHUNT COMPRISING A MAGNETIC CIRCUIT BETWEEN THE WINDING LEG AND THE SIDE LEG, ALL OF THE FILAMENT WINDINGS BEING COAXIALLY MOUNTED ON THE WINDING LEG ON ONE SIDE OF THE SHUNT AND ALL OF THE OTHER WINDINGS BEING COAXIALLY MOUNTED ON THE WINDING LEG ON THE OTHER SIDE OF THE SHUNT, WHEREBY THE FILAMENT WINDINGS AND THE OTHER WINDINGS HAVE A LOOSE MAGNETIC COUPLING WHICH WILL RESULT IN A SUBSTANTIAL PHASE ANGLE DIFFERENCE BETWEEN THE FILAMENT WINDING CURRENT AND THE SECONDARY WINDING CURRENT. 